Liquid scintillation counting and automated instruments known as liquid scintillation counters are widely utilized to analyze samples containing radioactively labelled substances.
Typically, a sample in solution is mixed with a liquid scintillator, commonly referred to as a cocktail, and the light events produced from the sample and cocktail mixture are detected according to their energy and number of events. The light events occur when the energy of the particles, emitted from the radioactive isotope component of the sample in solution, is transferred to the molecules of liquid scintillator. This produces a light emission of a specific energy range which is characteristic of the radioactive isotope.
Detecting both the energy and number of light events in a particular energy range provides the information necessary to construct a spectrum. Using this information the radioactive species can be quantitatively analyzed. Liquid scintillation counting and automated instruments to perform liquid scintillation counting have been widely discussed in a multitude of publications and patents.
Scintillation counting of liquid samples has certain disadvantages attributable to the nature of the liquid solution used. One is a phenomenon known as quench. Quench commonly refers to an effect in the scintillation process of a chemical or optical nature which results in loss of light events or reduction in light emission energy. The chemical nature of the solution in which the sample and scintillator are mixed and the color of the liquid sample solution are the causative agents. The result is inefficiency in the ability of the liquid scintillation counter to accurately count the particle disintegrations of the isotopes, and therefore interference with sample analysis.
Another disadvantage is that after analysis the liquid produced by mixing the radioactive sample with the cocktail must be disposed of. The regulations and controls governing the disposal of liquid radioactive materials are particularly rigorous. Due to the volume of liquid radioactive materials that require disposal of, the costs can be considerable.
In many cases a solid material having a radioactive nature is easier to dispose of and incurs less expense. Plastics are often used as such solid scintillation materials and previously mentioned in the literature are the thermosetting plastics which include polystyrene, polyvinyltoluene, various acrylic polymers and copolymers. The following patents further illustrate the use of plastics as scintillation materials.
U.S. Pat. No. 3,010,908 issued Nov. 28, 1961, discloses the use of dialkylstyrene polymers as the primary absorber in a solid solution scintillation counting composition.
U.S. Pat. Nos. 2,985,593 and 3,356,616 disclose styrene-derived monomers polymerized or copolymerized with vinyl or methacrylate monomers to form the solvent for a solid solution scintillation counting composition.
U.S. Pat. No. 3,457,180 issued July 1969 discloses as the solvent for a solid solution scintillator copolymerized paravinyltoluene and methylmethacrylate.
U.S. Pat. No. 3,513,102 discloses a fluorescent coating in which a fluor and a copolymer of an acrylate and styrene are dissolved in an organic solvent, and the solution is emulsified in an aqueous dispersion of a hydrophilic colloid. The copolymer is not derived from a latex, but is a solution polymer isolated, redissolved and blended by high-speed milling for dispersion in a gel binder.
U.S. Pat. No. 3,886,082 issued May 27, 1975 discloses an example of one such plastic scintillator material. The scintillator employs acrylic polymers and copolymers as the host plastic and bis(O-methylstyryl)-benzene, perylene, tetraphenyl-butadiene, diphenyl anthracene, bis(-phenyloxazolyl benzene) and dimethyl bis(phenyl oxazolyl benzene) as the fluorescent additive.
U.S. Pat. No. 4,180,479 issued Dec. 25, 1979 discloses the use of various stilbene derivatives as fluorescent agents in scintillators.
U.S. Pat. No. 4,495,084 discloses plastic scintillators in which a scintillating substance is incorporated into a matrix resin which comprises a copolymer of a styrene type compound and various unsaturated copolymers including unsaturated esters.
U.S. Pat. No. 3,068,178 discloses plastic scintillators based on polystyrene and polyvinyltoluene.
More recently there have been further advances in the field of solid scintillators.
U.S. Pat. No. 4,713,198 describes the preparation of a polymethylpentene thermoplastic scintillator capable of functioning at high temperatures.
International Patent application WO 90/16002 describes a detection material that is solid at room temperature but optionally meltable to fluid. This material is composed of a low molecular weight plastic, a hot melt copolymer and a paraffin wax.
U.S. patent application Ser. No. 07/499,434 refers to a solid-liquid reversible scintillator used for solid support sample counting. This scintillator is composed of fluors, paraffin and p-xylene and is fluid above 40.degree. C. but reverts to a translucent waxy solid upon cooling.
French Patent No. 1,590,762 describes the use of polyolefin resins and solvents to form gels which can be used as scintillation materials. These materials are solid-liquid reversible.
International Patent application WO 89/02088 describes the use of an inorganic solid scintillator which is attached to a solid support medium by a binder material.
U.S. Pat. No. 4,692,266 issued Sep. 8, 1987 describes a dry solid scintillator counting composition for the detection of radiative substances in a liquid.
U.S. Pat. No. 3,491,235 describes a method for producing fluorescent layers by dispersing organic solution of fluorescent compounds in aqueous colloid solution, coating and drying.
Japanese Patent Publication Sho 63-101787 describes multi-layer scintillators made by piling up either mixed monomolecular films consisting of radiation absorbing compounds and compounds emitting ultraviolet, visible or infrared radiation, or monomolecular films consisting of radiation absorbing compounds and separate monomolecular films consisting of compounds emitting ultraviolet, visible or infrared radiation. The layers are deposited from a solution of the compounds in chloroform.
U.S. Pat. No. 4,258,001 describes an element for analysis or transport of liquid, which contains a structure comprising a plurality of heat-stable, organo-polymeric particles non-swellable in and impermeable to the liquid, and an adhesive concentrated at particle surface areas contiguous to adjacent particles bonding the particles into a coherent, three-dimensional lattice that is non-swellable in the liquid. Interconnected void spaces among the particles provide for transport of the liquid.
The prior art scintillators have the disadvantage that it is not possible to cohesively bond them onto plastic support media. The plastic support media can be polystyrene, polyvinylchloride, polyethylene, polypropylene, other polyolefins, acrylonitrile copolymers and combinations of these. The plastic support media can also be clear, translucent, white or black or a combination of these. The plastic support media can be fabricated into microplates, petri dishes, culture flasks, test tubes and stand-alone single cups. As well as plastic support media, other media, e.g. glass and metals are suitable host support media. Further disadvantages of the prior art scintillators are that they do not possess the properties necessary for producing a scintillating plastic coating on a solid support medium.